Use Ubuntu18.04 (#31620)

* Use Ubuntu18.04

* Update .azure/pipelines/jobs/default-build.yml

Co-authored-by: Doug Bunting <[email protected]>

* Undo queue updates

Co-authored-by: Doug Bunting <[email protected]>

Author: wtgodbe

.azure/pipelines/ci.yml

@@ -566,7 +566,7 @@ stages:
       jobDisplayName: "Build: Linux Musl ARM64"
       agentOs: Linux
       useHostedUbuntu: false
-      container: mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-16.04-cross-arm64-alpine-20200413125008-406629a
+      container: mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-18.04-cross-arm64-alpine-20210311173921-b2c2436
       buildScript: ./build.sh
       buildArgs:
         --arch arm64
@@ -680,7 +680,7 @@ stages:
       parameters:
         condition: ne(variables['SkipTests'], 'true')
         jobName: Linux_Test
-        jobDisplayName: "Test: Ubuntu 16.04 x64"
+        jobDisplayName: "Test: Ubuntu 18.04 x64"
         agentOs: Linux
         isTestingJob: true
         useHostedUbuntu: false
@@ -734,12 +734,15 @@ stages:
     displayName: 'Test: Linux Source Build'
     container: centos:7
     pool:
-      vmImage: 'ubuntu-16.04'
+      vmImage: 'ubuntu-18.04'
     variables:
       DotNetCoreSdkDir: $(Agent.ToolsDirectory)/dotnet
       # This isn't needed in the path because build does not need to _use_ global tools.
       DOTNET_CLI_HOME: $(System.DefaultWorkingDirectory)
       DOTNET_SYSTEM_GLOBALIZATION_INVARIANT: true
+      LC_ALL: 'en_US.UTF-8'
+      LANG: 'en_US.UTF-8'
+      LANGUAGE: 'en_US.UTF-8'
     steps:
     - script: |
         source eng/common/native/common-library.sh

.azure/pipelines/jobs/default-build.yml

@@ -95,7 +95,7 @@ jobs:
         vmImage: macOS-10.14
       ${{ if eq(parameters.agentOs, 'Linux') }}:
         ${{ if eq(parameters.useHostedUbuntu, true) }}:
-          vmImage: ubuntu-16.04
+          vmImage: ubuntu-18.04
         ${{ if eq(parameters.useHostedUbuntu, false) }}:
           ${{ if eq(variables['System.TeamProject'], 'public') }}:
             name: NetCorePublic-Pool
@@ -139,6 +139,9 @@ jobs:
         - _SignType: real
       - ${{ if in(variables['Build.Reason'], 'PullRequest') }}:
         - _SignType: test
+    - LC_ALL: 'en_US.UTF-8'
+    - LANG: 'en_US.UTF-8'
+    - LANGUAGE: 'en_US.UTF-8'
     steps:
     - ${{ if ne(parameters.agentOs, 'Windows') }}:
       - script: df -h